4© Capt. Rater’s experiments for determining the 
serve as centres, to the sides of the elevated part of the support, 
and one end of this frame being raised or depressed by means 
of the screw A, the pendulum when placed with its knife edge 
resting in Ys, at the other end of the frame, could be elevated 
entirely above the surface of the agate, or be gently lowered 
until the knife edge rested wholly upon it, and thus the knife 
edge was sure to bear always precisely on the same part of 
the agate plane, by elevating the Ys, above its surface, placing 
the knife edge in them, and then letting down the whole 
gently by means of the screw, till the Ys were completely 
clear of the knife edge. The support was firmly screwed to 
a plank which will hereafter be described. 
To the kindness of Henry Browne, Esq. F. R. S., I am 
essentially indebted for the success of the experiments which 
form the subject of this paper. He most obligingly allowed 
me the use of his house, his excellent time-pieces, and transit 
instrument, assisting me with indefatigable zeal by his very 
accurate daily observations, and intermediate comparisons for 
determining the rate of the clock. The house is substantially 
built, and is situated in a part of Portland Place not liable to 
much disturbance from the passing of carriages. The room 
in which the experiments were made is the last of two on the 
ground floor, communicating with each other and facing the 
north. The temperature consequently is very steady, and if 
necessary, may be raised to any given degree by a fire in the 
first room. The clock with which the pendulum was com- 
pared was made by Arnold ; and in addition to the gridiron 
compensation for temperature, its pendulum is suspended by 
a spring, the strength of which is so adjusted, that the vibra- 
tions in different arcs are performed in equal times, This, 
